bims-ershed 2023-07-16 papers

Am J Pathol. 2023 Jul 06. pii: S0002-9440(23)00237-7. [Epub ahead of print]

Stress and Liver Fibrogenesis: Understanding the role and regulation of stress response pathways in Hepatic Stellate Cells.

Zachary Hanquier, Jagannath Misra, Reese Baxter, Jessica L Maiers.

Stress response pathways are crucial for cells to adapt to physiological and pathological conditions. Increased transcription and translation in response to stimuli places a strain on the cell, necessitating increased amino acid supply, protein production and folding, and disposal of misfolded proteins. Stress response pathways such as the Unfolded Protein Response (UPR) and the Integrated Stress Response (ISR) allow cells to adapt to stress and restore homeostasis; however, their role and regulation in pathological conditions such as hepatic fibrogenesis are unclear. Liver injury promotes fibrogenesis through activation of hepatic stellate cells (HSCs), which produce and secrete fibrogenic proteins to promote tissue repair. This process is exacerbated in chronic liver disease, leading to fibrosis and, if unchecked, cirrhosis. Fibrogenic HSCs exhibit activation of both the UPR and ISR, due in part to increased transcriptional and translational demands, and these stress responses play important roles in fibrogenesis. Targeting these pathways to limit fibrogenesis or promote HSC apoptosis are potential anti-fibrotic strategies, but are limited by our lack of mechanistic understanding of how the UPR and ISR regulate HSC activation and fibrogenesis. In this article we explore the role of the UPR and ISR in the progression of fibrogenesis and highlight areas that require further investigation to better understand how the UPR and ISR can be targeted to limit hepatic fibrosis progression.

Keywords: ATF6α; Cirrhosis; Endoplasmic Reticulum; GCN2; HRI; IRE1α; Integrated Stress Response; PERK; PRK; Unfolded Protein Response

DOI: https://doi.org/10.1016/j.ajpath.2023.06.006

Front Med (Lausanne). 2023 ;10 1124514

Inhibition of protein translation under matrix-deprivation stress in breast cancer cells.

Shweta Warrier, Shivaani Srinivasan, Adithya Chedere, Annapoorni Rangarajan.

Matrix-deprivation stress leads to cell-death by anoikis, whereas overcoming anoikis is critical for cancer metastasis. Work from our lab and others has identified a crucial role for the cellular energy sensor AMPK in anoikis-resistance, highlighting a key role for metabolic reprogramming in stress survival. Protein synthesis is a major energy-consuming process that is tightly regulated under stress. Although an increase in protein synthesis in AMPK-depleted experimentally-transformed MEFs has been associated with anoikis, the status and regulation of protein translation in epithelial-origin cancer cells facing matrix-detachment remains largely unknown. Our study shows that protein translation is mechanistically abrogated at both initiation and elongation stages by the activation of the unfolded protein response (UPR) pathway and inactivation of elongation factor eEF2, respectively. Additionally, we show inhibition of the mTORC1 pathway known for regulation of canonical protein synthesis. We further functionally assay this inhibition using SUnSET assay, which demonstrates repression of global protein synthesis in MDA-MB-231 and MCF7 breast cancer cells when subjected to matrix-deprivation. In order to gauge the translational status of matrix-deprived cancer cells, we undertook polysome profiling. Our data revealed reduced but continuous mRNA translation under matrix-deprivation stress. An integrated analysis of transcriptomic and proteomic data further identifies novel targets that may aid cellular adaptations to matrix-deprivation stress and can be explored for therapeutic intervention.

Keywords: ISR; SUnSET; mTORC1; matrix-deprivation; polysome; protein translation; stress; translatome

DOI: https://doi.org/10.3389/fmed.2023.1124514

Mol Cell. 2023 Jun 29. pii: S1097-2765(23)00467-7. [Epub ahead of print]

Enhanced SARS-CoV-2 entry via UPR-dependent AMPK-related kinase NUAK2.

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) remodels the endoplasmic reticulum (ER) to form replication organelles, leading to ER stress and unfolded protein response (UPR). However, the role of specific UPR pathways in infection remains unclear. Here, we found that SARS-CoV-2 infection causes marginal activation of signaling sensor IRE1α leading to its phosphorylation, clustering in the form of dense ER-membrane rearrangements with embedded membrane openings, and XBP1 splicing. By investigating the factors regulated by IRE1α-XBP1 during SARS-CoV-2 infection, we identified stress-activated kinase NUAK2 as a novel host-dependency factor for SARS-CoV-2, HCoV-229E, and MERS-CoV entry. Reducing NUAK2 abundance or kinase activity impaired SARS-CoV-2 particle binding and internalization by decreasing cell surface levels of viral receptors and viral trafficking likely by modulating the actin cytoskeleton. IRE1α-dependent NUAK2 levels were elevated in SARS-CoV-2-infected and bystander non-infected cells, promoting viral spread by maintaining ACE2 cell surface levels and facilitating virion binding to bystander cells.

Keywords: ACE2; CLEM; IRE1a ultrastructure; SARS-CoV-2; TMPRSS2; coronavirus; membrane dynamics; trafficking; unfolded protein response; virus entry

DOI: https://doi.org/10.1016/j.molcel.2023.06.020